6 urban legends that actually check out

You learned the basic health “don’ts” at an early age: Avoid cracking your knuckles (it causes arthritis), don’t swallow gum (it stays in your stomach for 7 years!), and never walk in winter with wet hair (you’ll catch a cold). Then you grew up and learned none of them were true, and brushed aside every urban health legend you ever heard.But just because carrots don’t actually help your vision, it doesn’t mean every tale your mom told you about your health was a lie. In fact, these six are legit.

1. YAWNING IS CONTAGIOUS.Research in monkeys, dogs, and humans has proved if one person yawns, so do those around him, says Steven Scharf, M.D., PhD., director of the University of Maryland Sleep Disorders Center. But the reason is as mysterious as the phenomenon. One possibility: Yawning increases alertness, so some speculate it’s contagious to help synchronize members of a group to be alert to the possibility of threats, Dr. Scharf says.

2. WANT TO GET RID OF YOUR HICCUPS? HAVE SOMEONE SCARE YOU.Hiccups happen when your diaphragm muscles and controlling nerves get stuck in a "reflex arc," where the nerves keep signaling the diaphragm to contract suddenly—causing your hiccup—and then triggering it to repeat itself, says Rachel Vreeman, M.D., M.S., coauthor of Don’t Cross Your Eyes ... They’ll Get Stuck That Way! And 75 Other Health Myths Debunked. This reflex usually ends on its own, but something that interrupts the loop—like being startled enough to gasp—can sometimes make the hiccups stop sooner, she adds.

3. A COLD SHOWER CAN SHAKE YOUR URGE FOR SEX.Not only will the shock of cold water provide an effective distraction, but the temperature also helps lower your heart rate, says Men's Health urology advisor Larry Lipshultz, M.D. The cold causes your blood vessels to narrow—known as vasoconstriction—which in turn, restricts the flow of blood to all extremities, including the penis.

4. EATING STANDING UP HELPS BURN OFF THE CALORIES YOU’RE CONSUMING.Studies show that standing burns 40 percent more calories than sitting. Over time it might give you an advantage, but the bigger problem is that people tend to eat differently when they are standing: “We often don’t pay as much attention to what or how much we’re eating, and end up making less-healthy choices and consuming more,” Dr. Vreeman says.

5. READING IN THE DARK WILL HURT YOUR EYES.Since the pupils of your eyes open wider in dim light, that makes it more difficult to focus on fine detail, such as reading, says Jeffrey Anshel, O.D., Fellow of the American Academy of Optometry, and President of the Ocular Nutrition Society.

The verdict is still out on whether it will affect long-term vision, he adds, but since it’s easier to read in good light anyway, don’t bother finding out if the damage would be permanent.

6. EATING JUNK FOOD BEFORE BED GIVES YOU NIGHTMARES.A few small studies have shown that people who ate sugary or spicy foods before bed also reported having awful dreams. But the sleepers might have remembered the terrors strongly—as you typically do with nightmares—and looked for something to blame them on, says Dr. Vreeman.

“If it is true, scientists think the higher levels of sugar might alter how the brain functions during sleep,” she explains, adding there’s no hard data yet showing how this would work.